The present invention relates to a method and apparatus for decoding a large crossbar switch array.
Crossbar switch arrays commonly find use on cathode ray tube (CRT) faces as overlays which provide a means for codifying information corresponding to an image on the CRT. The switches are commonly made by photofabricating a large number of horizontal switch lines on a plastic lamina and a large number of vertical lines on another lamina and sandwiching a perforated plastic lamina between the horizontal and vertical array laminas. The laminated switch assembly, which is transparent except for the switch lines, is then placed on the CRT. The cross-over points between horizontal and vertical switch lines act as switches which are closed by depressing one of the lamina to press the upper switch line into a perforation and against a line on the other lamina.
In switch arrays as described above, each horizontal and vertical line is connected to the outside by a discrete line which enters a discrete logic element for digital decoding of the position of the closed switch. Where the matrix of switch lines is large, it is impractical to bring each line off the laminate as would be required for external decoding. It is also impractical to provide a logic element for each line.